To assess the treatment effect of oral alendronate 10 mg/day versus placebo on the change in BMD of the spine when administered for up to 24 months in men with osteoporosis. To define the safety/tolerability profile of oral alendronate when administered in men with osteoporosis. To assess the treatment effects of alendronate 10 mg/day versus placebo on the change in hip and total body BMD when administered for 24 months in men with osteoporosis. To examine the effects of alendronate 10 mg/day on biochemical markers of bone turnover (urinary N-telopeptide crosslinks and serum bone-specific alkaline phosphatase) in men with osteoporosis. To examine the relationship between the changes in bone mass at the spine and baseline: (a) BMD, (b) biochemical markers of bone turnover (c) gonadal status (d) age (e) geographic location (U.S. vs non-U.S.) (f) renal function (g) height.